Reviewing volcanic halogen emissions

Volcanoes are a natural source of halogens for the atmosphere. After water, carbon dioxide and sulphur compounds, halogens are often the most common gases in volcanic plumes. Over the past two decades, progress has been made in the study of volcanic emissions, particularly those of the heavy halogens bromine and iodine. This contribution provides an interdisciplinary literature review on the current state of the art, and including also some unpublished data, in particularly with regard to bromine and iodine emissions. A detailed global emission estimate is provided, including an analysis of global distribution and comparison with different natural sources. Although volcanoes are point sources with sometimes very high halogen concentrations (mixing ratios in the ppb range), after all their global source strength is rather low compared to other natural halogen sources such as the ocean. The contribution of volcanoes to global halogen emissions into the atmosphere is only in the low percentage range, with the possible exception of extremely large eruptions. However, the spatial distribution of the emissions is quite inhomegeous, so that halogen emissions from volcanoes can still have a local and regional impact on the atmosphere that has not yet been sufficiently investigated.